MR. HAROLD MILLAR invites notes on this subject (NATURE, February 5, p. 600). The case of the crossbill (Loxia curvirostra, Linn.) seems in point. My attention was directed to it some years ago, when I saw a number of crossbills—six or eight, if I remember aright—confined in a large cage or small aviary at Glenferness, Nairnshire. The brilliant scarlet plumage which distinguishes the adult male in a state of freedom had changed on these captives to yellowish-olive, and I was informed that this was the invariable effect of captivity. The late Lord Lilford kept a number of crossbills in his famous aviary, and has the following note in his coloured “Figures of Birds of the British Isles”:—